1. Field of the Invention
This invention relates to a system for regulating the valve timing of an internal combustion engine, particularly to a system for regulating the valve timing of an internal combustion engine that regulates the close times of the intake valves of the engine in a range beyond the compression stroke start point (normally bottom dead center in terms of crankshaft angle).
2. Description of the Related Art
Japanese Patent Laid-open Gazette No. 8-121122, for example, teaches a prior art system for regulating the valve timing of an internal combustion engine of this type wherein the opening/closing times of the intake valves of the engine are changed by changing the camshaft rotation phase relative to the crankshaft. This system includes a housing that rotates synchronously with the crankshaft, a vane rotatable relative to a housing connected to the camshaft, an advance chamber whose volume is expanded by oil inflow to advance the rotation phase of the vane relative to the crankshaft, and a retard chamber whose volume is expanded by oil inflow to retard the rotation phase of the vane relative to the crankshaft. The system controls the inflow of oil to the advance chamber and the retard chamber to change the rotation phase of the camshaft for driving the intake valves relative to the crankshaft and thereby change the opening/closing times of the intake valves. When this type of valve timing regulation system is used, however, it sometimes becomes impossible to properly start the engine. In general, engine intake valve closing is effected at a rotation angle after (45 degrees after, for example) the time point at which the intake stroke ends and the compression stroke starts (normally at bottom dead center of the crankshaft) so as to utilize the inertia of the intake air for charging as much air-fuel mixture into the cylinder as possible. Therefore, if the next starting of the engine is conducted using the opening/closing timing in effect when the engine was stopped, proper engine starting may become impossible depending on the intake valve close timing. For instance, when the engine has completely cooled down and an attempt is made to start it with the intake valve close timing still retarded, starting may be difficult since the compression pressure at starting is apt to be insufficient owing to the intake valves being open even after the compression stroke has started. This problem is pronounced when the intake valve close timing of the engine is set on the retard side in order to reduce knocking/vibration or improve fuel economy.
On the other hand, when the engine is thoroughly warmed up and an attempt is made to start it with the intake valve close timing advanced, the compression pressure rises excessively and the engine is apt to vibrate violently upon starting.